1. Field of the Invention
The present invention relates generally to the field of diving rebreathers, and more particularly, to a closed circuit rebreather (CCR) devoid of an external counterlung and having novel scrubber and valve arrangements, as well as a compact modular design that permits side-mounting of the rebreather, among other features.
2. Background of the Invention
A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. By recycling exhaled gas as opposed to expelling it into the surrounding water, the volume of breathing gas used is reduced, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where humans cannot safely breathe from the atmosphere.
The main advantage of the rebreather over other breathing equipment is the economical use of gas. With open circuit scuba, the entire breath is expelled into the surrounding water when the diver exhales. A breath inhaled from an open circuit scuba system whose cylinders are filled with ordinary air is about 21% oxygen. When that breath is exhaled back into the surrounding environment, it has an oxygen level in the range of 15 to 16% when the diver is at atmospheric pressure. This results in an available oxygen utilization of about 25%, the remaining 75% being lost.
At depth, the advantage of a rebreather is even more marked. Since the generation of CO2 is directly related to the body's consumption of O2 (about ˜99.5% of O2 is converted to CO2 on exhalation), the amount of O2 consumption does not change, therefore CO2 generation does not change. This means that at depth, the diver is not using any more of the O2 gas supply than when shallower. This is a marked difference from open circuit systems where the amount of gas used is directly proportional to the depth.
Other advantages of rebreathers include a reduction of equipment size and weight carried by the diver, conservation of expensive diluent gases, lack of bubbles and bubble noise, minimization of the proportion of inert gases in the breathing mix, minimization of decompression requirements of the diver, and providing breathing gas at a comfortable temperature and moisture content, among other advantages.
Although designs may vary, the major components of a closed circuit rebreather typically include a gas-tight loop, gas source, carbon dioxide scrubber, means for controlling the mix, counterlung and optional casing. The gas-tight loop is the component through which the diver inhales from and exhales into. The loop consists of components sealed together with the diver breathing through a mouthpiece or mask. The mouthpiece/mask is connected to one or more tubes bringing inhaled gas and exhaled gas between the diver and the counterlung, which holds gas when it is not in the diver's lungs. The loop also includes the scrubber, which contains a carbon dioxide absorbent to remove from the loop the carbon dioxide exhaled by the diver. Attached to the loop is at least one valve allowing for the injection of gases, such as oxygen and perhaps a diluting gas from the gas source into the loop. There may also be valves allowing venting of gas from the loop.
Most modern rebreathers also include a system of very sensitive oxygen sensors that allow the diver to adjust the partial pressure of oxygen. This can offer a dramatic advantage at the end of deeper dives, where a diver can raise the partial pressure of oxygen somewhat at shallower depth in order to shorten decompression times, but care must be taken that the PP02 is not set to a level where it can become toxic, as research has shown that a PP02 of 1.6 bar is toxic with extended exposure.
In contrast to conventional closed circuit rebreathers, the particular rebreather disclosed herein is modular and therefore can fit any standard gear configuration adapted to mount a standard AL80 tank. The rebreather disclosed herein is advantageous in that it can be side-mounted and has no external counterlung, making it ideal and safer for diving in narrow, confined passages such as caves and wrecks. The rebreather according to the present invention provides further advantages over the prior art designs including, but not limited to, novel scrubber and valve arrangements, which are described in detail below.